The ram accelerator is a relatively new method for achieving ultra high projectile launch velocities.
The concept was first described as early at 1966 in U.S. Pat. No. 3,253,511 issued to Zwicky, which patent is incorporated herein by reference. As described in the Zwicky patent, a body such as a projectile is located in an elongated tube in which it can slide easily yet fits closely enough to the inner wall to prevent ignition of the propellant ahead of the body. The propellants are introduced into the elongated tube and are ignited or reacted behind the projectile as the projectile passes through the propellants which are distributed along the entire length of the path along which acceleration of the particular body takes place. It may be noted that the body may be any type of projectile, including a vehicle and that alternatively the gases may be ignited within a thrust chamber in the projectile. As used herein, "projectile" is intended in its broad sense and may include bullets or other ordinance or vehicles or payloads which one may wish to accelerate. When combustion behind the projectile is referenced, it is understood that combustion within a combustion chamber within the projectile, but behind the front of the projectile, is included when the projectile is so designed.
Ram accelerators are similarly described in U.S. Pat. Nos. 4,658,699; 4,722,261 and 4,726,279, all of which are similarly incorporated herein by reference.
It has been known that if initial pressure of the combustible gas in a tube used to ram accelerate a projectile, could be elevated prior to ignition, better performance could be obtained due to an initially higher concentration of combustible materials.
Development work performed at the University of Washington at initially elevated combustible gas pressure has successfully achieved projectile velocities in excess of 2.0 kilometers per second when applying the accelerator concept, which is based on ramjet principals, to a projectile with an initial velocity of about 1 kilometer per second. While this work is still in the initial stages, performance estimates indicate that projectile velocities in the range of 5 to 10 kilometers per second or higher may be achieved. Velocities of this magnitude are of extreme interest for SDI and various conventional armament applications that are unique to the three services.
The work at the University of Washington has incorporated an accelerator charged with a combustible gas mixture at a specified pressure. The tube is sealed at both ends with a diaphragm which is ruptured by a projectile as it passes through the tube. This test configuration is useful for technology development testing under laboratory conditions and for potential single-shot applications.
Unfortunately, the use of diaphragms to enable increasing combustible gas pressure in the accelerator tube has significant disadvantages. In particular, the time to replace diaphragms does not permit rapid fire requirement of Gatling gun systems to be utilized. Furthermore, diaphragms, by their nature, do not permit high pressures to be used. If stronger tube closures to obtain higher pressures are used, the impact between the projectile and the closure becomes significant thus slowing or deflecting the projectile or even causing damage to the projectile or the tube. Gate valves can similarly not easily be used to close the exit of muzzle of the tube because such valves under rapid fire conditions are still too slow, would cause significant vibration and timing to prevent destructive contact of the projectile with the gate would be critical.